In a substrate processing apparatus used in fields of application pertaining to the present invention, a specific type of processing such as film formation or etching is executed on a target substrate to undergo processing (hereafter simply referred to as a substrate), which may be a semiconductor wafer or a liquid crystal substrate, by using a specific gas supplied into a processing chamber.
Such a substrate processing apparatus may be, for instance, a plasma processing apparatus. The plasma processing apparatus may include a lower electrode also used as a stage on which a substrate is placed and an upper electrode also used as a showerhead through which the gas is injected toward the substrate, both disposed within the processing chamber. In a plane parallel plate type plasma processing apparatus such as this, plasma is generated by applying high-frequency power to the space between the two electrodes while supplying the specific gas onto the substrate placed inside the processing chamber through the showerhead and the specific type of processing such as film formation or etching is executed with the plasma thus generated.
It has been a matter of crucial importance in the related art to improve the planar uniformity achieved through the specific substrate processing, such as film formation or etching executed on the substrate by assuring consistent substrate surface processing characteristics such as the etching rate, etching selection ratio, the film formation rate or the like.
Japanese Laid Open Patent Publication No. H08-158072 (patent reference literatures 1) and Japanese Laid Open Patent Publication No. H09-045624 (patent reference literatures 2), for instance, address this need by proposing that the space within the showerhead be partitioned into a plurality of gas chambers, that gas supply pipings be connected to the individual gas chambers independently of one another and that a processing gas of a given type or at a given flow rate be supplied to each of a plurality of areas within the substrate surface. The art disclosed in patent reference literatures 1 and 2 makes it possible to improve the planar uniformity achieved through a substrate etching process by adjusting the gas concentration at the substrate surface in units of the individual local areas.
The gases used in the actual substrate processing include a plurality of types of gases such as a processing gas that directly affects the substrate processing, a gas used to control deposition of reaction products resulting from the substrate processing and a carrier gas such as an inert gas selected in a specific combination so as to best suit the material on the substrate undergoing the processing or the specific processing conditions. For this reason, a mass flow controller must be installed for purposes of flow rate control in correspondence to each of the gas supply pipings connected to the individual gas chambers in the showerhead, as disclosed in patent reference literature 2.
However, such a structure in the related art, which includes a gas supply system in correspondence to the gas to be supplied from each gas chamber even if the gases used for different purposes may contain a common gas constituent, necessitates flow rate control to be executed separately for the gas supplied from each gas chamber. This is bound to result in a complex piping structure and require complex flow rate control for the individual pipings, necessitating, for instance, a large piping space and leading to a significant increase in the control onus.
In addition, even if the gases can be supplied through simple control from a plurality of areas within the processing chamber, the desired level of planar uniformity must be assured by ensuring that the control does not allow any fluctuation of the flow rate ratio (divided flow ratio) of the processing gases supplied from the various positions that may occur due to, for instance, a fluctuation of the pressures with which the gases are drawn in. In other words, the gas supply must be controlled without being affected by pressure fluctuations or the like.